A semiconductor module in which the semiconductor device is installed via a solder layer on a metal block and a resin is molded to cover the semiconductor device is known.
In such a semiconductor module, as is known from JP2004-186622A, for example, plural of square-shaped concave portions are arranged with a substantially equal distance apart in length and width directions on a portion of a surface of the metal block except for a semiconductor device installation area on which the semiconductor device is installed in order to increase stability in solder thickness directly underneath the semiconductor device as well as degree of adhesion between the metal block and the resin.
However, since the area on which the semiconductor device is installed is not subject to surface treatment such as plating, it is easily oxidized, which leads to such a problem that strict management of temperature and relative humidity or reduction treatment is required to ensure solder wetability. Further, if the metal block is pure Cu, CuSn is formed as an intermetallic compound at the time of soldering, which leads such a problem that Kirkendall voids are generated.
Therefore, in order to solve such problems, it is proposed that the surface of the metal block as a whole be Ni plated, as disclosed in JP2003-124406A, for example.
However, adhesion is not good between the Ni plating and the resin, and thus the resin may be peeled off the metal block. When the resin may be peeled off the metal block, there is such a problem in term of reliability that cracks or the like appear in the solder layer. For this reason, a primer such as an expensive polyamide resin or the like is coated on the area of the metal block on which the resin is to be formed in order to ensure adhesion between the resin and the metal block whose surface as a whole is Ni plated, which leads to an increase in manufacturing cost.